A pacemaker of this type is known for instance from EP 0 882 469 B1.
Implantable pacemakers are either operated using unipolar pacemaker electrodes or using bipolar pacemaker electrode. In the case of a unipolar electrode, the electro tip of the pacemaker electrode operates as a cathode and the pacemaker housing as an anode. The bipolar systems correspond to the unipolar systems insofar as they also operate using a cathodic electrode tip. Unlike unipolar systems, in the case of bipolar pacemaker electrodes, an anode is arranged however in the distal electrode region.
Complications can result both in the case of unipolar pacemaker electrodes as well as in the case of bipolar pacemaker electrodes, if the patient wearing the pacemaker is exposed to an intense magnetic field. Intense magnetic fields of up to 7 Tesla result particularly with magnetic resonance devices. If the magnetic field is changed, and/or the pacemaker electrode moves in the magnetic field, currents are induced which can cause the pacemaker electrode to heat up, thereby resulting in irreversible tissue damage. On this account, according to the prior art, patients with a pacemaker cannot be examined in magnetic resonance devices.
US 2003/0140931 A1 discloses a medical implantable system for reducing magnetic resonance effects, in which the electric circuit is interrupted as a function of a measured magnetic field, with the magnetic field being determined by means of a special magnetic field sensor.